1. Field of the Invention
The present invention relates to a lighting device with variable irradiation angles and a picture taking device using the lighting device, and the lighting device is preferably used, for example, in an optical instrument such as a video camera, film camera, or a digital camera in which the lighting device is mounted on part of a body of a camera (picture taking device) and achieves efficient irradiation toward a subject to take pictures by varying an irradiation angle of illuminating light (flash) in association with picture taking operations of the camera body according to a purpose.
2. Description of the Related Art
Conventionally, various proposals have been made for lighting devices used in picture taking devices such as cameras with the intention of efficiently collecting luminous flux emitted in various directions from a light source into a required irradiation view angle. Particularly, in recent years, instead of a Fresnel lens surface disposed in front of a light source, a proposed lighting device has an optical member utilizing total reflection such a prism light guide disposed for achieving techniques include switching between optical paths by inserting or rotating a divergence member or a reflection member in synchronization with forward-and-backward motions of a front panel in a direction along an exit optical axis, changing optical paths by a prism formed integrally with a front panel, and the like.
Proposed lighting devices provided with an optical member utilizing total reflection such as a prism light guide disposed in front of a light emitting means to achieve improved light collecting efficiency and a reduced size and to allow variable irradiation angles include an example as shown in the aforementioned Japanese Patent Laid-open No. 4-138439 having a light collecting optical system which has, in front of a flash emission unit, upper and lower two surfaces for causing luminous flux emitted mainly to the side of a light source to make incident to an optical member and then totally reflecting the luminous flux for collecting light in a predetermined direction, and a surface with positive refractivity formed in front separately from the two surfaces to collect light. The light collecting optical system collects light exit through the respective surfaces and then makes the light exit toward a subject from the same exit surface. A positional relationship between the optical prism and the light source is relatively changed to switch between reflection and improved efficiency of light collection and a reduced size.
On the other hand, picture taking devices tend to have higher power zoom. When a lighting device with a fixed irradiation range is used for such a picture taking device, illumination is performed in the maximum irradiation range even in tele mode which requires only a narrow irradiation range, thereby causing a large energy loss. To eliminate this drawback, lighting devices with variable irradiation angles have conventionally been proposed for illumination in accordance with a picture taking range.
As a known technology of a lighting system to which the aforementioned two kinds of techniques are applied, Japanese Patent Laid-open No. 4-138439 employs a light collecting optical system having an optical prism for totally reflecting light in which a positional relationship is relatively changed between the optical prism and a light source to switch between refraction and total reflection on a surface, and thus an irradiation range is varied. In Japanese Patent Laid-open No. 8-262538, a plurality of separate optical prisms are used and the optical prisms disposed at upper and lower positions are rotated to switch between irradiation ranges.
In addition, for varying an irradiation angle in a longitudinal direction of a light source, proposed transmission on the total reflection surface, thereby varying an irradiation range.
On the other hand, Japanese Patent Laid-open No. 8-262538 (U.S. Pat. No. 5,813,743) has proposed a lighting device in which a plurality of separate optical prisms are used and the optical prisms disposed at upper and lower positions are rotated to switch between irradiation ranges.
Any of the aforementioned techniques, however, fundamentally utilizes forward-and-backward motions of the front panel in the direction along the exit optical axis of the optical member to allow light condensing and diverging effects in a vertical direction. Thus, a disadvantage occurs in that the size is inevitably increased.
From the foregoing situations, it is an object of the present invention to provide a lighting device with variable irradiation angles which has small size yet significantly changes light condensing and diverging degrees in a vertical or horizontal direction efficiently by taking a shape for efficiently functioning in accordance with each state of condensed and diverged light, and a picture taking device using the lighting device.
It is also an object of the present invention to provide a lighting device with variable irradiation angles which is configured to require no space for an optical member to retract in its movement in varying an irradiation angle to extremely reduce the size of the whole configuration of a lighting optical system and continuously changes the ratio between areas where light is condensed and diverged to allow a continuous change in light distribution characteristic at each zoom point, and a picture taking device using the lighting device.
In one aspect according to the present invention, a lighting device is provided which comprises:
an illuminating light source for illuminating an object;
a first optical unit disposed on the side of the object of the illuminating light source and having an optical action section for diverging light or an optical action section for converging light; and
a second optical unit disposed on the side of the object of the optical action section of the first optical unit and having an optical action section for exhibiting a characteristic opposite to a characteristic of the optical action section of the first optical unit,
wherein the optical action section of the second optical unit overlies the optical action section of the first optical unit in varying areas to change light distribution characteristic on the side of the object.
Especially, the illuminating light source is a discharge tube having a longitudinal direction.
The second optical unit is moved in the longitudinal direction of the discharge tube to change the area where the optical action section of the second optical unit overlies the optical action section of the first optical unit when light distribution characteristic is changed.
The optical action section of the first optical unit has a plurality of convex portions or a plurality of concave portions arranged in a direction perpendicular to the longitudinal direction and the optical action section of the second optical unit has a plurality of concave portions or a plurality of convex portions having an optical characteristic opposite to an optical characteristic of the plurality of convex portions or concave portions.
The plurality of convex portions or plurality of concave portions of the first optical unit are a plurality of cylindrical lenses and the plurality of concave portions or plurality of convex portions of the second optical unit are a plurality of cylindrical lenses.
The plurality of convex portions or plurality of concave portions of the first optical unit are a plurality of toric lenses and the plurality of concave portions or plurality of convex portions of the second optical unit are a plurality of toric lenses.
A surface of the first optical unit on the side of the object has a region where the optical action section is formed and a region where the optical action section is not formed. A surface of the second optical unit on the side of the first optical unit has a region where the optical action section is formed and a region where the optical action section is not formed. Light distribution characteristic is changed by changing the area where the optical action section of the second optical unit overlies the optical action section of the first optical unit.
Other features will become apparent from the following description and accompanying drawings.